Hydraulic fracturing of the shelf is a process of pumping liquid into given oil and gas bearing underground shelves transverse to a well under pressure and at a rather high speed, in the result of which this shelf collapses and liquid penetrates a formed fissure. To maintain fissures open-ended after removal of rupture pressure a propping agent is added to pumped liquid which penetrating the fissure and filling it up functions as lining. In the result of hydraulic fracturing of the shelf oil and gas recovery factor in the well increases due to an increase in the total shelf area joining with the well, appearance of a larger pressure differential between the oil-bearing stratum and fissure stimulating oil or gas inflow to it, greater permeability of the fissure filled with prop as compared to the permeability of underground oil and gas-bearing rock.
A propping agent is high-strength spherical granules able to endure exposure to high temperature and pressure as well as aggressive environment (acid gases, saline solutions) created in the underground shelves near oil and gas wells.
U.S. Pat. No. 4,068,718 describes a propping agent obtained from sintered bauxite the specific gravity of which is over 3.4 g/cm3. It is stated that this specific gravity is necessary for an agent's particle not to be destructed even with high compressive efforts. However, the described material being rather solid and destruction-proof has great specific gravity which makes it inconvenient in use since it requires application of ruptural liquids with increased viscosity and leads to a low volume concentration of this agent in them. It results in a decrease in the width of a fissure after relief of rupture pressure and an insignificant increase in oil and gas recovery factor in the well.
U.S. Pat. No. 4,427,068 describes a propping agent propping agent with the specific gravity of 2.7-3.4 g/cm3 produced from a mixture of preliminarily fully or partially calcinated diaspore clay and dense nonplastic non-soaking fireproof clay (the so called, flint fireclay) with preliminarily roasted bauxite so that the ratio of alumine to silicon in this mixture constitutes from 9:1 to 1:1. Source materials are reduced to fine particles by dry method, are mixed in an Eirich mixer with powder corn starch. Then water is added to the mixer in the amount sufficient to form spherical compositional granules from powder mixture. The author maintains that the speed of adding water is not important. The granules are dried and baked in the rotating oven. The drawback of this invention is the restrictions of the used for prop fabrication natural aluminosilicate raw material since its use with the aluminum oxide content over 50% is required.
Also a mixture for fabrication of granules is known (RF patent No. 2140875), which contains (wt. %) 70-99.5 of kaolin roasted at 700-900° and 0.5-30% with the content of 30-45 wt. % of Al2O3, and 0.5-30% of an additive from the group of substances or their mixtures: bauxite roasted at 800-1100° C. and unroasted one, baddeleyite, powder zirconium concentrate, alumina dust as the wastes of alumine production. The amount of an additive depends on its nature and chemical content: alumina dust, the wastes of alumine production, containing Al2O3 99.0-99.5 wt. %, is added in the amount of 5.0-20.0 wt. %; baddeleyite containing ZrO2 91.0-96.0 wt. % , is added in the amount of 0.5-5.0 wt. %; powder zirconium concentrate containing ZrO2 60.0-65.0 wt. % is added in the amount of 0.5-10.0 wt. %; roasted at 800-1100° C. and unroasted bauxite containing over 65-75 wt. % is added in the amount of 5.0-30.0%; a mixture from alumina dust and unroasted bauxite in the ratio of 1:2 is added in the amount of 15 wt. %; a mixture of unroasted or roasted at 800-1100° C. bauxite and baddeleyite in the ratio of 1:9 is added in the amount of 10.0 wt. %; a mixture of unroasted bauxite and powder zirconium concentrate in the ratio of 1:4 is added in the amount of 10.0 wt. %; a mixture of alumina dust, bauxite roasted at 800-1100° C. and unroasted one in the ratio of 1:2:1 is added in the amount of 20 wt. %; a mixture of alumina dust and bauxite roasted at 800-1100° C. in the ratio of 1:1 is added in the amount of 10 wt. %.
The drawback of this mixture is the use of rather scarce and costly materials, most of which (baddeleyite, zirconium concentrate, alumina dust) are the products of natural raw material processing. The use of costly raw material increases the product's prime cost. The use of multicomponent mixtures complicates production workflow, requires a large number of intermediate containers, extra dosing equipment which additionally increases a product's prime cost and reduces the reliability of maintenance of the given production flow parameters, and leads to instability of end product characteristics. Addition of zirconium bearing components (baddelayite and powder zirconium concentrate) increases agent's specific gravity and bulk weight. In the result of using kaolin as the main raw material, the agent with the intermediate specific gravity (2.67-2.87 g/cm3) and bulk weight (1.67-1.89 g/cm3) is produced.
An offered mixture for fabrication of high-strength spherical granules allows to remove the said drawbacks and get a light prop with the specific gravity of 2.6-2.8 g/cm3 and bulk weight of 1.58-1.68 g/cm3 preserving its capability to endure exposures to high temperature and pressure as well as aggressive environment in the underground shelves near oil and gas bearing wells.
A method is known according to U.S. Pat. No. 4,921,820 where a preliminarily roasted at the temperature not lower than 900° C. kaolinite clay containing at least 1% of Fe2O3 and less than 2% of free quartz together with amorphous silicon is reduced in a ball crusher to the particles with the average size not smaller than 7 mkm. The mixture of a combined grind is granulated in the mixer, produced granules are dried and roasted.
The drawback of this method is the restrictions of the used natural aluminisilicate raw material since the use of kaolinite clay with the content of less than 1% of Fe2O3 and less than 2% of free quartz is needed. The use of costly amorphous silicon increases the product's prime cost.
The offered manufacturing method of high-strength spherical granules allows to remove these drawbacks.
The above and other features of the invention including various novel details of construction